I have torn down multiple Li-Ion laptop batteries, and have multiple cell phone cells. Most say 3.7 volt, though one says 3.8 volts. It appears they are all good for 3.0 to 4.2 volts best I have been able to determine, though I have been "survival charging" them to 3.9 volts @ 300mA to check them. My question is about what I can get away with. For parasitic load applications, would it be best to maintain 4.2 volts (and ballast current) once the cell is charged, or should I drop it down around 4.0 volts or take it off, and boost it back up when I'm ready to use my project battery only for awhile? Either way, I know more than 4.2 volts, even at 1uA, is destructive.
Proper Li-Ion handling
- Thread starter Lectraplayer
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I have looked at that one. They advise the charger cut off once charging is done, but I have devices that leaves 4.2 volts applied to the battery when it's charged. They seem to use the same theory I have (and am trying to research) that once the battery saturates at this voltage, it is pretty much an open circuit until charging input falls.
It also says that all the way up before storage is also hard on them, but some of these batteries have sat for years and still have 4.1 volts per cell. The ones that were somewhat drained now has 1.5 volts per charge, which gets the survival charge to 3.9 volts for evaluation. (I will not try to saturate them until I can put it on a purpose made charger)
It also says that all the way up before storage is also hard on them, but some of these batteries have sat for years and still have 4.1 volts per cell. The ones that were somewhat drained now has 1.5 volts per charge, which gets the survival charge to 3.9 volts for evaluation. (I will not try to saturate them until I can put it on a purpose made charger)
It totally depends on the cell that you have. There should be some numbers that you can google and find the spec sheet. I have torn apart many laptop packs. most are 4.1V, but can be tolerated at 4.2 but that will reduce it's life. I have some found cells that have a 4.35 spec.
If they dont reach 4.1 easily, and tend to heat up then they probably have developed internal shunting and might not be safe to use!
If they dont reach 4.1 easily, and tend to heat up then they probably have developed internal shunting and might not be safe to use!
I figured that much. I can survival charge a battery and it stays cold.
Back to my question earlier: will it harm my battery to leave my 4.1 volts or so on it?
Back to my question earlier: will it harm my battery to leave my 4.1 volts or so on it?
That is what I'm looking at doing, though I gathered that my voltage should stay below saturation.
How hard is that on them, to maintain a less than saturated voltage from an external source?
Good question. It depends on your load and power source. If the load is not requiring more than the charging source provides then battery will be charging. In situations where the load is not consuming current, just be sure to have a protection on the battery so the load doesn't destroy the batteries by overcharging. Or, not enough supply will overdischarge which is just as bad.
This is accomplished a charge controller. There are quite a few types of them.
This is accomplished a charge controller. There are quite a few types of them.
I'd say it wont be too bad on them as long as you're not exceeding the current ratings of the battery. laptop cells are usually rated for 0.5C charging. So a 2200 mah battery shouldn't be charged at greater than 1.1 Amps. Some are less. The good ones are rated for higher currents (ie tesla cells).
I have mostly Panasonic and Sony cells. Also, I keep hearing .8C and 1C, though I typically stay in the neighborhood of .25C to .8C. Since my load will be 400mA and my charger 750mA @ 4.0 volts on a 1875mA/h battery, that sounds like a winning example doesn't it?
